P2P search system usually be integrated to many systems in wired network. As the result of technology development, wireless networks are more and more popular. Many system in wired networks are be implemented in wireless network environment, too. In virtue of diverseness between wired and wireless networks, there are some modify for characteristic of wireless network. In this paper, we demonstrate KAdHoc, a peer-to-peer search system for Mobile Ad Hoc Network (MANET).There are problems when P2P systems being used in MANET such as physical locality, power exhaustion and nodes information outdated when nodes move. KAdHoc consider these problems and design a mechanism for P2P search system in MANET. The simulation result show that KAdHoc has fewer lookup time and has high success rate and low total traffic even in High Node density. KAdHoc even has higher success rate in higher node velocity.

This paper presents a DHT-based grid resource indexing and discovery (DGRID) approach. With DGRID, resource-information data is stored on its own administrative domain and each domain, represented by an index server, is virtualized to several nodes (virtual servers) subjected to the number of resource types it has. Then, all nodes are arranged as a structured overlay network or distributed hash table (DHT). Comparing to existing grid resource indexing and discovery schemes, the benefits of DGRID include improving the security of domains, increasing the availability of data, and eliminating stale data. / Singapore-MIT Alliance (SMA)

Made available in DSpace on 2014-06-12T15:51:58Z (GMT). No. of bitstreams: 1 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Diversos trabalhos na área de redes dinâmicas têm sido propostos na literatura com o objetivo de prover à arquitetura da Internet o suporte à mobilidade. O problema dessas redes instáveis na Internet consiste em oferecer um conjunto de mecanismo, tais como endereçamento, gerenciamento da informação e encaminhamento da informação, que suportem informação e entidade (Sistema Autônomo, Provedor de Serviços na Internet e Clientes) móveis. Nesse contexto, alguns trabalhos para arquitetura da Internet têm proposto uma maneira de separar a localização (atualmente o IP) e o nome identificador, devido ao forte relacionamento entre o IP e o nome. Em geral, eles propõem uma abordagem de roteamento na camada overlay para separar essas informações. Outros trabalhos acreditam que este desacoplamento não é suficiente para solucionar os problemas de mobilidade, desde que a dinamicidade gera muitas mensagens de controle e atualizações do vínculo entre o IP e o nome. Por essa razão, os pesquisadores também têm proposto novos modelos para gerenciar a camada overlay. Uma das contribuições deste trabalho é a proposta de uma solução para arquitetura da Internet denominada Stable Society que adota a abordagem de papéis. Um papel é uma unidade funcional que é utilizada para organizar a comunicação. Um importante diferencial da proposta é que além de desvincular o nome e a localização, ela também oferece soluções para os problemas relacionados a estruturação e manutenção da camada overlay. Além disso, este trabalho define quatro papéis: o mensageiro encaminha os dados dentro da sociedade; o guarda é a entidade mais estável para encaminhar mensagens entre as sociedades; o operário armazena informações; e o líder estrutura e gerencia a rede overlay. Reduzindo o escopo para a implementação desta dissertação de mestrado, o mensageiro e o guarda foram considerados como a camada de rede sem distinção de estabilidade, desde que o fornecimento de um mecanismo de gerenciamento do overlay de roteamento foi o objetivo do trabalho. Portanto, como prova do conceito apresentado pela proposta, os líderes e operários foram implementados, porque eles agem de maneira independente de tecnologia de acesso e são fundamentais para solucionar o problema da instabilidade nos processos de armazenamento e descoberta da informação. Como resultado, um novo algoritmo denominado Stable Society model over Distributes Hash Table (SSDHT) foi proposto. Além disso, este algoritmo foi comparado com outras soluções DHT (Chord). Os resultados mostraram que o SSDHT é um bom algoritmo, principalmente quando se aumenta a instabilidade (carga do tráfego, grau de mobilidade e tamanho da rede). Por exemplo, a taxa de mensagens entregue com sucesso foi acima de 90% quando a carga de tráfego, o grau de mobilidade e o tamanho da rede foram variados

The thesis investigates deployment of a Peer-to-Peer storage system in a cluster environment, in which machines have good and persist network connection, in order to provide the functionality of a data centre. For various reasons, the implementation is based on the Peer-to-Peer system known as Chord. Chord naturally provides storage load-balancing, especially if its virtual node scheme is used, but this needs to be improved if Chord is used to implement a storage system. A novel, threshold-based storage load-balancing scheme is proposed. Each machine in the system contributes a fixed amount of disk storage space to the Peer-to-Peer storage system. The system commences operation in the normal Chord manner except that two distinct sets of tables are initialised, one to maintain the usual Chord Ring, and one to maintain proximity information about the machines in the system. As files are inserted, the collective storage space gradually fills up. When any machine reaches the threshold for usage of its contributed space, the system behaviour is modified. Attempts are made, repeatedly if necessary, to migrate virtual nodes from heavily loaded machines to less-heavily loaded machines elsewhere in the system. The proximity information is used so as to minimise the costs of this migration. The nature of the proximity information is complex, and a Space-Filling Curve is utilised to reduce the complexity. For reasons of effectiveness, demonstrated by an evaluation against other kinds of Space-Filling Curve, the Hilbert curve is specifically chosen. The performance of the resulting implementation is evaluated in a practical experimental environment which consists of five teaching laboratories in the author’s school. Under the specific conditions of the experiments, the new system achieves significantly better distribution of storage utilisation across the participating machines and also defers the onset of unreliable behaviour in the system. In one experiment, the amount of the total storage space available that is actually utilised by the system increased from ∼ 43% to ∼ 62% using the proposed mechanism. The parameters used in the experiments have been chosen somewhat arbitrarily, so it is possible that even better results might be feasible.

DHT sistemų privalumas yra jų didelis plečiamumas ir nepriklausomumas, tačiau esami paieškos sprendimai reikalauja išorinių mechanizmų ir taip mažina DHT privalumus. Šio darbo tikslas – padidinti paieškos DHT sistemose galimybes, sukuriant vidinį paieškos mechanizmą Chord algoritmo pagrindu veikiančiai DHT sistemai ir ištiriant jo efektyvumą. Šiame darbe pristatomi galimi vidinės paieškos mechanizmai DHT sistemose pagrįsti n-gramomis ir užtvindymo pranešimais mechanizmu. Tyrimas parodė, kad n-gramos labiau tinkamos sistemoms, kurių dydis yra santykinai mažas, tuo tarpu užtvindymo mechanizmas priimtinesnis sistemose, kuriose įgyvendintas duomenų replikavimas. / The key idea of DHT systems is hash table distributed over the distributed independent nodes. The DHT are decentralized, scalable, fault tolerant and have high hit guaranties for data lookup. However, they do not support arbitrary querying which flooding schemes do: users must know exact key of the resource they are looking up in the system. In the most common solution for this is external searching engine like ftp or http. This work presents research experiment of possible methods for arbitrary querying in DHT based on the “n-grams” and “broadcasting” techniques. Experiment was carried out using experimental P2P system created for this purpose on the base of Chord algorithm. Experimental results showed that, the most expensive (in terms of message generation) process in “n-gram” is publishing of keys to network. The analysis of both methods showed that n-grams are more practical on the relatively smaller network and “broadcasting” is more effective on the networks with implemented data replication.

Paskirstytos maišos lentelės modeliai ir jų saugumo problemos yra aktyviai nagrinėjama sritis akademinėje bendruomenėje. Šiame darbe keliama hipotezė, kad praktinės DHT tinklų realizacijos neužtikrina teoriniuose modeliuose priimtos sąlygos, kad mazgų prisijungiančių prie tinklo identifikatoriai bus generuojami atsitiktinai. Randamas atakų sudėtingumo įvertis, kai atsitiktinių identifikatorių generavimas yra privalomas ir kai identifikatorius galima pasirinkti laisvai. Hipotezės patvirtinimui atliekamas eksperimentas. Surenkami ir analizuojami vieno didžiausių DHT tinklų (BitTorrent DHT) duomenys. Aprašomas literatūroje siūlomas problemos sprendimo būdas ir praktinės problemos kylančios jį realizuojant. Pasiūlomas naujas praktiškai pritaikomas ir našus identifikatorių generavimo patikrinimo metodas bei metodas naujų identifikatorių generavimo greičiui DHT tinkle valdyti. / Distributed Hash Table models and its security implications, has long been a subject of interest. This thesis is based on the assumption that practical implementations do not enforce random node id generation regardless of the fact that theoretical models require node ids to be chosen by random and distributed in the address space uniformly. To measure the impact on the DHT network security if the assumption holds an analysis of attack complexity in both cases is performed. Results indicate that the complexity grows from O(1) to O(M) if the node id cannot be selected arbitrarily (M is the number of nodes in DHT network). Stated assumption is confirmed by analysing classic node id protection methods and performing analysis of BitTorrent DHT network. The reason for the lack of node id protection in practice is considered to be the complexity and performance penalty of the classic methods. To facilitate the implementations of DHT networks a new method to ensure random node id generation and copy protection is provided. Proposed method utilizes MACs based on shared keys to provide a proof of the ownership of the node id while still providing means to protect it from being copied. Efficiency of the proposed method is evaluated by conducting an experiment. In order to protect small DHT networks against a Sybil attack a method to control the speed of node id generation is also proposed.

Une des problématiques majeure de sécurité pour les opérateur est de permettre à ses utilisateurs de maintenir la sécurité d’une communication même au travers d’un réseau qui ne soit pas de confiance. Pour l’utilisateur, une communication est établie entre deux identifiants, et ceci indépendamment des mouvements et changements de réseau de l’utilisateur. Autrement dit, l’opérateur doit permettre cette communication entre identifiants possible grâce au système DNS, et fournir les mécanismes réseaux nécessaires afin que la communication puisse être maintenue quand le client bouge et change d’adresse. Dans cette thèse nous nous somme concentrés sur les aspects sécurités et plus exactement: - DNSSEC: DNSSEC définit comme sécuriser la résolution d’un nom de domaine. La sécurité a un coût que nous commençons par évaluer avant de proposer des architectures permettant aux ISPs de migrer des plateformes de Service de Résolution de DNS vers DNSSEC. - IPsec: IPsec définit comment sécuriser une communication IP. Dans cette thèse nous définissons une extension qui permet à un utilisateur de maintenir une communication sécurisée par IPsec pour un terminal mobile, Multihomé, et avec de Multiples Interfaces / ISPs are concerned about providing and maintaining the level of security of its End User’s communications. A communication is initiated by the End User with a name, and goes on by exchanging packets between two IP addresses. In this thesis, we focused our attention on two main points: (1) providing a secure Naming service, and (2) making IPsec communication resilient to IP address modification, addition or lost of an interface. We designed MOBIKE-X for that purpose and propose it as a standard at the IETF

In dynamic P2P networks, nodes join and depart from the system frequently, which partially damages the predefined P2P structure, and impairs the system performance such as basic lookup functionality. Therefore stabilization process has to be done to restore the logical topology. This paper presents an approach to relax the requirement on routing tables to provide provably better stability than fixed structured P2P systems. We propose a relaxed Chord that keeps the O(logN) number of hops for greedy lookup, but it requires less stabilization overhead. It allows a tradeoff between lookup efficiency and structure flexibility without adding any overhead to the system. In the relaxed routing structure, each routing entry ("finger") of the node is allowed to vary within a set of values. Each node only needs to keep a certain number of fingers that point to nodes in its anchor set. This relaxation reduces the burden of state management of the node. The relaxed routing scheme provides an alternative structure other than randomized P2P and deterministic P2P, by relaxing on finger selection. It provides good flexibility and therefore extends the system functioning time. / Singapore-MIT Alliance (SMA)

Fully distributed systems offer the highest level of freedom for the users. For this reason, in today’s Internet, it is recorded that more than 50% of the packets moving in and out belong to this type of network. Huge networks of this kind are built on the top of DHTs, which follow a more structured communication compared to the other small peer-to-peer networks. Although nature always favors freedom and independ-ence, security issues force consumers to set up their network in a cen-trally controlled manner. One of security threats posed on such net-works is lookup attacks. A lookup attacks are kind of attacks which targets on disrupting the healthy routing process of the DHTs. Even though the freedom of peer-to-peer networks comes at the cost of securi-ty, it is quite attainable to make the network more secure, especially, it is quite achievable to gain performance on this level of attack according to the experiments carried out in this thesis. The secure routing techniques introduced have been found to outperform those without the techniques under investigation. The simulation performed for default Chord overly and the modified Chord, yielded interesting results, for dropper nodes, random lookup routs and colluding sub-ring attacks.

Distributed hash tables (DHTs) have gained much attention from the research community in the last years. Formal analysis and evaluations on simulators and small-scale deployments have shown good scalability and performance. In stark contrast, performance measurements in large-scale DHT overlays on the Internet have yielded disappointing results, with lookup latencies measured in seconds. Others have attempted to improve lookup performance with very limited success, their lowest median lookup latency at over one second and a long tail of high-latency lookups. In this thesis, the goal is to to enable large-scale DHT-based latency-sensitive applications on the Internet. In particular, we improve lookup latency in Mainline DHT, the largest DHT overlay on the open Internet, to identify and address practical issues on an existing system. Our approach is implementing and measuring backward-compatible modifications to facilitate their incremental adoption into Mainline DHT (and possibly other Kademlia-based overlays). Thus, enabling our research to have impact on a real-world system. Our results close the performance gap between small- and large-scale DHT overlays. With a median lookup latency below 200 ms and a 99\superscript{th} percentile of just above 500 ms, our median lookup latency is one order of magnitude lower than the best performing measurement reported in the literature. Moreover, our results do not show a long tail of high-latency lookups, unlike previous reports. We have achieved these results by studying how connectivity artifacts on the underlying network ---probably caused by firewalls and NAT devices on the Internet--- affect the DHT overlay. Our measurements of the connectivity of more than 3 million nodes reveal that connectivity artifacts are widespread and can severely degrade lookup performance. Scalability and locality-awareness have also been explored in this thesis, where different mechanisms have been proposed. Some of the mechanisms are planned to be integrated into Mainline DHT in future work. / QC 20111118